Two years ago I bought my refractometer at the annual winemaking-gig at Brouwland in Belgium. Since then I always said I wished I had bought it long before.In the many stories on this web-log you can see that I do all measurements with my hydrometer as welll as with the refrctometer. I use both instruments side by side.

A refractometer is more expensive as a hydrometer, it has however some significant advantages. The time has come to do some in-dept review so the winemakers amongst us that have no experience with a refractometer get some insight.Maybe this story is the motive to justify such an expensive purchase, or helps this story explain to your loved ones why you want such an instrument for your birthday, fathers- or mothersday, or as a chrismast gift.........

The theory

How the refractometer works is based on an easy to understand and demonstrate principle. Everyone knows that a spoon submerged in a glass of water seems broken. That is because the light-rays are bend-off in water.

Now when you dissolve a lot of sugar in the water the break will seem much bigger. The photo shows this somewhat. In the glass on the right side the fork looks more broken as in the glass on the left side.

So, as the SG of the fluid rises the break will look bigger.Now if we would be able to project that break on a scale you could read the SG value. And that is just what a refractometer does.The refractometer.

The photo shows you a standard refractometer. This is my own.

At the fron side you can see a glass plate covered with a plastic lid. Behind that an adjustment screw and on the left side the part weher you look through.

Modern digital camera's have a fantastic macro function. My somewhat older Nikon 2100 also has that function. Now when I put the camera in macro function and press the lens against the refractometer I can instantly make pictures from the measurements. That is an ideal feature not only for my web-log but also for record keeping in my winemaking log........

Calibrating

Any serious measuring instrument needs to be calibrated before use. Meaning it must be adjusted to a certain reference point.

When using a hydrometer you always need to cool down (or warm up) the juice you are testing to the temperature the meter is calibrated for.

Now there are two types of refractometers around. When you are going to buy one, do yourself a favor and buy the one with ATC.

ATC is an abrivation for Automatic Temperature Correction.This means that you do not need to wait till the temperature of the to be tested fluid is at a certain level. The refractometer will correct itself for the temperature deviation. That saves a lot of time and effort.

Off course you can not put a boiling hot fluid on the glass plate, it will surely crack. Nor could you measure an icecube..... Do all things with good judgement.

When looking through the refractometer without a fluid on the glass plate you will see a completely blue screen.

Now put just a drop of ditilled water on the plate and close the plastic lid. This makes sure that the fluid is evenly divided on the glass plate. Wait about 30 seconds and you will see this:

Naturally the SG of distilled water is 0, we did not expect anything else.

Now when your reftactometer shows a different value you know it is not calibrated.We know for sure that distilled water has an SG of 0, so the reftactometer is not calibrated if it shows something else.Now using the supplied screwdriver you can slowly turn the calibration screw. Turn it until the division line between the blue and white part is at the 0-line as the photo shows.

I own my refrctometer for 2 years now, and I only had to calibrate it once.

When you wear glasses, or your eyes are not as good as they used to be you can turn at the ocular to get a sharp image, just like using binoculars.

Measuring in daily life.

If you want to test the SG of a juice or must you will fill a testing tube and let the hydrometer float in it.

As most of us use this method for testing SG you will know that you will need quit a bit of juice for this purpose. Most testing tubes have to be filled with 250ml must. And before you can do the measurement properly you will have to chill (or warm) the juice to a certain level the hydrometer needs for doing the measurements right.

For a measurement using a refractometer you will need just 1 tiny drop of juice which you can obtain with a pipette from the bottle, carboy or bucket. And like said before there is no need to adjust the temperature.

So if you are walking through your vinyard or orchard or through the strawberry fields/blackberry fields/elderberry bushes or fill in yourself whatever kind of fruit, you can crush just one berry and will know the SG within a few seconds !!!

Below you will find some examples of measurements done both with the hydrometer and the refractometer so you can see for yourself how they indicate the SG values.

As you will know from experience a hydrometer is often difficult to read.A refractometer will clearly show the SG value. Even easier to see if you take a picture which you can magnify with the lcd screen of the camera or enlarge it by printing.The scale

There are refractometers available with different scales. In the US and Great Brittain they often are equipped with the Brix scale.

Brix is the percentage sugar that is present in a fluid. For us Europeans that is not very interesting. But for countries with pre-historic measurements like cups, quarts, gallons etc. this is the easiest to work with.

I prefer a refractometer with the Oechsle scale. The Oechsle scale is the same as the SG scale where 1000 is subtracted from. So an SG of 1080 is represented in the refractometer with an oechsle scale as 80. 1050 will be 50. And 1000 will be shown as 0.

Often refractometers have a double scale: Oechsle and % alcohol. The percentage alcohol that my refractometer indicates is never used by me. I always just use the Oechsle scale.Beware !!!

A hydrometer measures the weight (to be exact Specific Weight) of a fluid. A refractometer does not. He just measures the bending of lightbeams.

I will give you here an example:

Dissolve 50 gram sugar in exact 1 liter water.

A measurement taken with the hydrometer as well as with a refractometer will both show you an SG of 1020.

Now dissolve 50 gram citric acid in exact 1 liter water.

The hydrometer will again show an SG of 1020. The refractometer however will show an SG of 1015. This is because the bending of light will be different in a solution of sugar in water as in a solution of acid in water.

For normal daily use this has no consequence, however tjhere is an exception.

Measuring SG in a fermenting must

Some winemakers think it is necesarry to constant (daily) measure the SG of their fermenting must during winemaking. I am not one of these.

However they think it is necesarry to do daily measurements of their must to follow the fermentation progress. Well you CAN NOT DO THIS JUST LIKE THAT with a refractometer.

As soon as a must is fermenting, alcohol will form.Now alcohol alters the bending of light which will inhibit the accurate function of the refractometer.Actually it is the same that happens when measuring water with acid, like we have seen above.

So is the refractometer not usable in that situation ???Well there is a solution for everything. And many have given considerable thought about this problem.

In the US a spreadsheet has been published in which you can fill out the refractometer measurements. The spreadsheet will calculate from that the real SG values so you can follow the fermentation process.There is just one small disadvantage: the spreadsheet uses Brix values.You can download the spreadsheet by clicking here.To use it you will need to have Microsoft Excell or for the Linux minded Open Office.

If there are enough of you that are really interested I can transform this spreadsheet to one more suitable for SG (oechsle) values. If you do want this, send me an e-mail. When I get enough response (in my opinion) I will give it a go.

However I sincerely think that if you feel the need to measure the SG of all your fermenting musts on a daily base you are still a beginner without a clue of what real winemaking is about. I can however see the need for a daily measurements for some specific reasons.

So what is the alternative ???

I personally only measure SG when preparing a must. After this I never measure SG again. I will KNOW when a wine has finished. I can however imagine that beginners are lost at this.

So there is a way to measure the SG of a fermenting must with a refractometer. You will have put some effort in this.

Take an exact known amount of must, for example 20ml.Now boil this down to about half the volume and then refill it with distilled water to exact the orioginal volume.Now you will have a must from which the alcohol has been removed. Take a drop our and measure the SG with the refractometer.

I already adressed this method on this web-log within another context: measuring residual sugar. You can find that story by clicking here.Maintenance.

A refractometer does not require a lot of maintenance.A piece of kitchenpaper or a soft cloth is best to clean the glass plate after each measurement. Make sure it is a soft cloth because you do not want to scratch the surface of the glass.

Summarising

In short I will list the advantages and disadvantages of a refractometer.

Advantages:- You just need 1 drop of fluid to do the measurement- The temperature does not have to be exact 20 degrees celsius- Easy to do the readings- Easy to clean- Fast

Disadvantages:- More expensive as a hydrometer- Less suitable for continuous SG reading in a fermenting must or to determine the end-SG.

Conclusion.

A refractometer is a very handy instrument. Once I wrote that I found it a pity that I did not buy it years ago, and I still underwrite that statement. For my web-log I will use the hydrometer and refractometer next to eachother. I will do that for clarity for you, my readers, as not everyone is used to a refractometer.

For field surveys in a vineyard, orchard or garden the refractometer is ideal. You just squeeze some fruit, put a drop of juice on the refractometer and you have an immediate SG reading. This is impossible with a hydrometer.

For testing a fermenting must a refractometer is less suitable. You will have to do calculations using a spreadsheet, or boil off the alcohol to get the right readings.

In the end.......

There is a method that uses a hydrometer AND a refractometer reading from a finished wine, does some calculations, and so derives the alcohol percentage from the wine. I am not going to telle that story here as I am planning to do a series on alcohol measurement on this web-log. So stay tuned !!!!